1. Field of the Invention
The present invention relates to a method of manufacturing in a continuous process a flexible multi-layer compound structure having a controlled perviousness, and also to means for carrying out this method. This invention is applicable more particularly to the manufacture of wall coverings.
2. The Prior Art
Especially during the last decade, double-width textile wall coverings have become increasingly popular for lining and decorating main-and partition walls. These coverings may consist either of a simple fabric or, in most instances, of compound structures comprising a cloth or a sheet of yarns or fibres bonded to one or a plurality of flexible substrata by means of a pasting or welding process. In many cases these substrata consist of foam webs or sheets, or of thermoplastic films. These wall coverings, manufactured in widths slightly greater than the standard height of house walls, i.e. in widths of the order of 2.7 to 3 meters, can be put up either according to the tension laying method, i.e. by using staples and slightly stretching the wall covering on a frame having its side disposed along the edges of the wall, or according to the paste-and-stretch method, i.e. by pasting locally along stripes about one or two inches wide disposed along the wall edges.
Hitherto known wall coverings may be divided into two main types:
on the one hand, wall coverings which do not constitute a barrier to air and water vapor, and are sometimes referred to as open-cell coverings, and
on the other hand, wall coverings constituting a barrier preventing the passage of air and water vapor, which are sometimes referred to as closed-cell coverings.
Open-cell wall coverings are those whose composition is free of any film, sheet or continuous layer or web capable either singly or in combination to prevent the passage of air or water vapor through the coverings.
Included in this range of products are plain fabrics or coverings consisting of a cloth welded by calendering to an open-cell foam sheet by means of a thermoplastic net inserted between the cloth and the foam.
Due to their air-perviousness, these open-cell wall coverings are liable to retain on their surface atmospheric dust forming a deposit by filter effect. This clogging up becomes rapidly visible and is therefore particularly detrimental in the case of light-colored coverings.
As a counterpart of the inconveniences resulting from the accumulation of dust by filter effect, open-cell wall coverings are advantageous in that the walls to which they are applied can `breath`, so that the humidity likely to spread on the wall surface for example by capillary propagation from the house foundations or basement can evaporate continuously.
The composition of closed-cell coverings comprises one or more continuous films, sheets or layer capable either singly or in combination of preventing the passage of air or water vapor through the covering. Such coverings are notably those consisting of cloth welded to a sheet by means of a continuous and relatively thick thermoplastic film inserted between the cloth and the foam, or alternatively wall coverings having a continuous film pasted to their back face. Closed-cell wall coverings through which air cannot pass are free of the above-mentioned inconvenience of dust clogging caused by filter effect.
On the other hand, impervious coverings are objectionable in that they prevent the natural evaporation of the humidity spreading on the wall surface. This is most likely to cause serious damages such as for instance the accumulation of humidity within the walls, which develops mildew and consequently the disintegration of the binder and the spreading of moisture up to the ceilings of the rooms involved.
It is thus clear from the foregoing that a choice should be made between totally impervious and totally pervious wall coverings, with all the advantages and inconveniences resulting therefrom.
Besides, it should be noted that these perviousness or imperviousness properties are also considerably important for other applications such as packing materials, seat upholstery, materials used in the making of shoes, garments and else.